This Fire Opal contains both Opal and the rhyolitic host material in which it is formed, which provides sufficient hardness for the stone to be cut. The name “Fire Opal” is derived from the translucent fiery oranges and reds for which the Opal is known, though it also can occur in dark brown and golden colors. Some specimens of Fire Opal produce iridescent flashes and are referred to as Precious Fire Opal or “Firmament Stone.”